Optically variable security devices

ABSTRACT

An optical device is formed by hot stamping a demetallized hologram to an optically variable foil or to a coating of optically variable ink. In another embodiment a hologram is hot stamped to a banknote or document printed with a color-shifting ink.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly assigned and co-pendingU.S. Pat. Application Serial No. 16/425,532, filed May 29, 2019, whichis a divisional of commonly assigned and co-pending U.S. Pat.Application Serial No. 14/644,556, filed Mar. 11, 2015, which is adivisional of U.S. Pat. Application Serial Number 13/250,480, filed Sep.30, 2011, which is a continuation-in-part of U.S. Pat. Application Ser.No. 11/682,059 filed Mar. 5, 2007, which claims priority from U.S.Provisional Application No. 60/861,608 filed on Nov. 29, 2006, U.S.Provisional Application No. 60/832,826 filed on July 24,_2006, U.S.Provisional Application No. 60/744,842 filed on Apr. 14, 2006, and U.S.Provisional Application No. 60/779,484 filed on Mar. 6, 2006, which areincorporated herein by reference for all purposes. U.S. Pat. ApplicationSerial Number 13/250,480 is a continuation-in-part of U.S. Pat.Application Ser. No. 11/738,855 filed on Apr. 23, 2007, which claimspriority of U.S. Provisional Application No. 60/747,142 filed May 12,2006. Application Ser. No. 11/738,855 is a continuation-in-part of U.S.Pat. Application Ser. No. 11/682,059 filed Mar. 5, 2007, which claimspriority from U.S. Provisional Application No. 60/861,608 filed on Nov.29, 2006; U.S. Provisional Application No. 60/832,826 filed on Jul. 24,2006; U.S. Provisional Application No. 60/744,842 filed on Apr. 14,2006; and U.S. Provisional Application No. 60/779,484 filed on Mar. 6,2006, which are incorporated herein by reference for all purposes. Theseapplications are all incorporated herein by reference for all purposes.

All patents and patent applications mentioned heretofore and hereafterare incorporated herein by reference, for all purposes.

FIELD OF THE INVENTION

The present invention is related generally to hot-stamping and moreparticularly, to the production of an optical device by hot-stamping adiffractive and optically variable portions of the device together.

BACKGROUND OF THE INVENTION

U.S. Pat. 6,987,590 in the name of Phillips et al., discloses an opticaldevice that includes a light transmissive substrate having a surfacerelief pattern applied thereon, in the form of a hologram. Infabricating this optical device a patterned layer of a reflectivematerial is applied over portions of the surface relief pattern so as toform alphanumeric characters, bars codes, or pictorial or graphicaldesigns. An optically active coating is deposited or applied as an inkor paint over the patterned layer of reflective material and exposedportions of the surface relief pattern in order to provide desirableoptical effects to the exposed portions of the surface relief pattern.In some embodiments, the optically active coating is a color shiftingthin film, or contains color shifting flakes. Optionally, the materialof the optically active coating is index matched to the lighttransmissive substrate in order to optically erase the effect of thesurface relief pattern in the portions of the surface relief pattern notcovered by the reflective material. This aforementioned patentapplication provides an optical structure having a light transmissivesubstrate having a surface relief pattern formed thereon; a patternedlayer of a reflective material applied onto portions of the surfacerelief pattern of the light transmissive substrate, such that someportions of the surface relief pattern are covered by the reflectivematerial, and other portions of the surface relief pattern are exposed.The structure further has an optically active coating underlying thepatterned layer and exposed portions of the surface relief pattern. Thisstructure is a type of chromagram.

The term chromagram used hereafter is meant to include opticalstructures that have a patterned or windowed substrate together withspecial effect coatings or layers supported by or supporting thepatterned or windowed substrate. Chromagrams of various designs areknown from our patent applications and used as security devices or forenhancing the security of products and for their aesthetic appeal.

By use of the term “patterned” layer, it is meant that a reflective,opaque, or partially transmissive layer is applied over a substratewhich may be planar or have a surface relief pattern therein, in amanner that forms a desired “pattern” or design. By way of non-limitingexamples, the patterned reflective layer can be formed in the shape ofletters, numerals, bar codes and/or graphical or pictorial designs.

One type of chromagram is an optical structure that exhibits the effectsof stamped or etched surface relief patterns, such as holograms ordiffractive gratings together with a pattern such as alphanumericcharacters, bar codes, or graphical or pictorial designs, and additionaloptical effects in the regions around such pattern. Such structures aredescribed in U.S. Pat. Application 2006077496 in the name of Argoitia etal. published Apr. 13, 2006. Another chromagram-type structure isdescribed in U.S. Pat. Application 20050128543 in the name of Phillipset al. In this publication patterned substrates having windowed regionsthat one can see through, are coated with optically variable coatings oroptically variable inks that can be seen through the windows. For allintents and purposes, all references described heretofore or hereafterare incorporated herein by reference.

U.S. Pat. Application 20070058227 in the name of Raksha et al.,discloses an optical device comprising a hologram and a layer ofcolor-shifting magnetically aligned flakes together forming an imagethat is difficult to counterfeit and is highly attractive. Optionally, atransparent diffractive grating is laminated to a magnetically formedimage.

Although not limited thereto, this invention primarily relates to typesof Chromagrams that combine security features of a hologram and a colorshifting layer conveniently joined by an adhesive layer. This inventionalso relates to chromagrams having a windowed or patterned substrateadhesively joined to a layer of foil.

A key aspect of such chromagrams is that one layer having transmissiveregions and some optical feature such as a hologram or a patternedopaque or patterned partially transmissive regions is hot stamped toanother layer, web or substrate that has optical features that can beseen through the windows. This is a significant departure from prior artChromagrams and windowed optical structures. Of course hot stamping, adry process, is well known, however is typically used to hot stamp adevice or security device such as a hologram to an object or substrate.Hot stamp transfer foils have been provided in conjunction with hotstamp machines to affix images onto various substrates such as paper,plastic film and even rigid substrates.

One commercially available machine for hot stamping images ontosubstrates is the Malahide E4-PK produced by Malahide Design andManufacturing Inc. Machines of this type are shown and described on theInternet at hotstamping.com. Simplistically, in a hot-stamping process,a die is attached to the heated plate which is pressed against a loadroll of hot stamping foil to affix the foil to an article or substrate.

Hot stamping is described or mentioned in the U.S. Pats. 5,002,312, US5,059,245, US 5,135,812, US 5,171,363, US 5,186,787, US 5,279,657 and7,005,178, in the name of Roger Phillips of Flex Products Inc. of SantaRosa Ca.

A novel and inventive aspect of this invention is to provide a processand device made by the process for fabricating a security device, byusing hot stamping to make the security device, which may then befurther hot stamped to an object or substrate.

Heretofore chromagrams or layered security devices have been fabricatedby depositing or coating one layer of material over another onto asubstrate. Generally, such process would be done in a singlemanufacturing facility. However, is has been discovered that somefacilities are better equipped or have persons better skilled atproducing some coatings and substrates, than others. For example we havefound that some off-shore manufacturing facilities produce excellentwindowed or reflective patterned substrates and also have staff veryskilled in the manufacture of holograms or diffraction gratings withinthe substrate supporting the windowed coating. We have also found thatour facility in the United States produces very high quality coatingsand pigments such as optically variable foils and flakes.

This invention provides a means for manufacturing a first coatedsubstrate in one location and a second coated substrate in a secondlocation and marrying together the two coatings to form a single opticaldevice that can be applied to a substrate or object. A novel aspect ofthis invention is that one of the coatings is adhesively bonded to thesecond coating by way of hot stamping in such a manner as to allow afirst coating to be visible through windows or uncoated regions in thesecond coating. This is a significant departure from the way in whichthese optical structures were formed in the past, where each of thelayers were coated one after the other to form the desired chromagram.

It is another object of this invention, to provide a hot stamp imagewith multilayer security features.

SUMMARY OF THE INVENTION

A method is provided for manufacturing a device. The method includes: a)providing a diffractive structure for forming at least a portion of animage; b) providing an optically variable structure separate from thediffractive structure, for providing an optically variable feature tothe image; c) covering the diffractive structure or the opticallyvariable structure with an adhesive, wherein the adhesive comprisesenergy activated binder; and d) after steps (a)-(c), activating theadhesive and coupling the diffractive structure and optically variablestructure together in a predetermined mutual arrangement, wherein theenergy activated binder forms an adhesive layer.

In accordance with one aspect of this invention, a device is provided,comprising: a diffractive structure for forming at least a portion ofthe image; an optically variable structure for providing the opticallyvariable feature to the image; and an adhesive layer for coupling thediffractive structure and optically variable structure in apredetermined mutual arrangement. The adhesive between the diffractivestructure and the optically variable structure is an internal adhesivelayer of the device. Additionally, an external adhesive layer may beprovided to the diffractive structure or the optically variablestructure for attaching the device to an object.

In accordance with another aspect of this invention, a method forforming a device is provided, comprising the steps of:

-   a) providing an optically variable foil;-   b) covering the optically variable foil with an adhesive;-   c) providing a hologram adjacent to the adhesive; and-   d) hot stamping the hologram and optically variable foil together by    heating the adhesive while applying pressure to the hologram and    optically variable foil.

In an embodiment of the instant invention an adhesive material on ade-metalized surface of a hologram is followed underneath with anoptically variable ink that has already been applied to the banknote orsubstrate.

In an embodiment of this invention optically variable ink is firstprinted on a substrate followed by hot-stamp process bonding togetherthe optically variable ink layer with a substrate having a windowedhologram.

In yet an alternative embodiment banknote or document has hot stampedthereon a demetallized hologram, wherein the hot stamp adhesive hasoptically variable flakes mixed therein in direct contact with thedemetallized surface of a hologram.

In an aspect of the invention the optically variable ink can be seenthrough portions of the de-metalized hologram or where both can be seenat the same time.

In accordance with the invention there is provided a demetallizedhologram or windowed hologram hot stamped on to an optically variablefoil.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof that areillustrated in the appended drawings. It is to be appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 a is a cross sectional drawing illustrating the manufacture of aportion of chromagram in accordance with the teachings of thisinvention.

FIG. 1 b is a cross sectional drawing illustrating the manufacture of aportion of chromagram in accordance with the teachings of thisinvention.

FIG. 2 a is a cross-sectional view of a Chromagram with an adhesivebetween an optically variable (OV) foil and demetallized hologram.

FIG. 2 b is a cross-sectional view of a Chromagram with an adhesive.

FIG. 2 c is a cross-sectional view of a Chromagram with a clear adhesivebetween the foil and demetallized hologram, wherein the adhesivecontains covert flakes or a low concentration of optically variableflakes or optically variable magnetic flakes.

FIG. 2 d is a cross-sectional view of a Chromagram wherein an OVstructure includes a laser ablated insignia.

FIG. 2 e is a cross-sectional view of a Chromagram according to anotherembodiment of this invention.

FIG. 3 a is a cross-sectional view of a Chromagram wherein a grating issupported by, or formed therein, a layer of high refraction indexmaterial.

FIG. 3 b is a cross-sectional view of a Chromagram wherein a demethologram is supported by, a layer of high refraction index material.

FIG. 4 is a cross-sectional view of a Chromagram wherein an OV structureis adhesively bonded to the substrate supporting a diffractivestructure, whereas the OV and diffractive structures are coupled bypressure.

FIG. 5 is a view of a poker chip made in accordance with the inventionwherein covert flakes having symbols thereon are provided within thecoating in a similar manner to FIG. 2 c .

DETAILED DESCRIPTION

The present invention is related to optical devices wherein a reliefstructure providing an optical effect such as a hologram or diffractiongrating is coupled to an optically variable structure by an adhesive,which may be an energy activated adhesive. The resulting opticalstructure exhibits unique optical effects.

For the purpose of this application, the term “energy activatedadhesive” or “energy activated binder”, means a bonding substance thatrequires an energy source for curing. The energy activated adhesivesinclude, but are not limited to, hot stamp adhesives, UV or e-beamactivated adhesives, thermoplastic and thermoset adhesives, paint-basedpolymeric compositions, varnishes, and staining compositions. By way ofexample, an adhesive is selected from the group of: polymethacrylate,polyacrylate, polyamide, nitrocellulose, alkyd resin, polyvinyl alcohol,polyvinyl acetate, and polyurethane.

The methods of activating the adhesives include hot stamping, UV curing,applying heat, pressure, or a beam of electrons. For brevity, an energyactivated adhesive, possibly with special flakes therein, is referred toas “an adhesive” hereinbelow where it does not lead to confusion.

As was described heretofore, in the background of the invention, thefield of hot stamping and more particularly, hot stamping of one opticalcoating or substrate with another is well known. For example, coatedsubstrates bearing images, logos or other indicia are hot stamped ontolottery cards, passports, banknotes, driver’s licenses, poker chips, anda variety of other articles and substrates are well known.

The adhesive may be printed into patterns or flood coated over theentire surface. If patterned, the product becomes more tamper proofsince the product cannot be physically removed in one piece. Attempts toremove the device by dissolving the adhesive using solvents would alsobe detrimental since the solvent would also attack the hardcoat/releasewhich in turn would destroy the device, making tampering obvious.

The device disclosed in the present application comprises a diffractivestructure, which can take various conventional forms includingdiffraction patterns such as diffraction gratings, refraction patterns,holographic patterns such as two-dimensional and three-dimensionalholographic images, demetallized holograms, coatings with varied indexof refraction, light transmissive dielectric coatings with refractiveflakes therein or thereon, Kinegram^(R) devices, Pixelgram^(R) devices,corner cube reflectors, zero order diffraction structures, moirépatterns, and light interference patterns based on microstructureshaving dimensions of from about 0.1 µm to about 10 µm.

In accordance with one embodiment of the present invention, thediffractive structure comprises a reflector layer, having at least apart demetallized. A demet layer can be made of Al, Cu, Ni, and othermetals and metal alloys that have been patterned by demetallization.Various techniques may be used to pattern the metal layer, such aschemical etching or oil ablation in vacuum, both done in registrationwith the relief image.

In one embodiment of the present invention, the diffractive structurecomprises a windowed or segmented opaque layer having one or more lighttransmissive windows to allow combining of optical effects provided bythe diffractive and optically variable structures, so that the opticallyvariable structure is visible through said windows when the device isviewed from the side of the diffractive structure. Preferably, thewindowed coating is reflective to provide an additional securityfeature.

The diffractive structure may be embossed on an embossable resin layermade of such materials as type G PET, Polycarbonate, polyvinyl chlorideor polymethacrylate. An embossable layer may be combined withhardcoat/release layer. An embossing may be either patterned orcontinuous.

The diffractive structure may comprise a grating formed in a substrate,preferably a light transmissive or essentially transparent substrate,which may be made of Polyethylene Terephtalate (PET), OrientedPolypropylene (OPP) or other suitable plastic material. By way ofexample, a PET layer has a thickness of 6-25 microns.

The diffractive structure may comprise a high refraction index layercoated on a relief pattern, such as an embossed resin layer. The highrefraction index layer may be made of a material having the index ofrefraction no less than 1.65. A high refractive index layer can be madeof ZnS, TiO₂, ZrO₂, etc.

In one embodiment of the present invention, the diffractive structure isvisible through the OV structure, so the substrate supporting thediffractive structure may be opaque.

In one embodiment of the present invention, the diffractive structure isa windowed substrate having a coated pattern thereon, wherein regionsthat are uncoated form windows therethrough the color shiftingbackground is visible.

The device disclosed in the present application comprises an opticallyvariable structure which, in one embodiment, is a multilayer opticalinterference film comprising a reflector layer, an absorber layer, and adielectric layer between the reflector and absorber layers, as it isknown in the art. A reflective layer can be made of any metal that has areflectance over 20%, preferably aluminum. By way of example, adielectric layer is made of MgF₂ or other transparent material as knownin the art.

An absorber can be a grey metal with a ratio of n/k about 1, where n isthe real part of the refractive index and k is the imaginary part of thereflective index, for example Cr or Ni or other transition metal, or canbe a non-selective absorber across the visible spectrum, or can be acermet, as described in the article entitled “Influence of NanosizedMetal Clusters on the Generation of Strong Colors and Controlling oftheir Properties through Physical Vapor Deposition (PVD)” by R. Domnicket al., 49th Annual Technical Conference Proceedings (2006), Society ofVacuum Coaters, incorporated herein by reference. By way of example, acermet material comprises silver islands in a dielectric matrix.

In another embodiment of the present invention, the optically variablestructure is a multilayer optical interference film comprising a firstand second absorber layers, and a dielectric layer therebetween. Thismultilayer film configuration is disclosed in U.S. Pat. No. 5,278,590 toPhillips et al. Such a film structure allows optically variablestructure 10 b to be transparent to light incident upon the surfacethereof.

In yet another embodiment, the optically variable structure is amultilayer optical interference film comprising alternating low and highrefraction index layers, where the individual layers have an index ofrefraction between 1.38 and 2.3

In one embodiment of the present invention, the optically variablestructure comprises a light transmissive dielectric coating with aplurality of multilayer optical interference flakes therein or thereon.Such flakes are described, for example, in U.S. Pat. No. 6,749,777granted to Argoitia et al.

Alternatively, the optically variable structure comprises opticallyvariable ink, comprising optical effect flakes in a carrier, wherein theflakes may have one or more predetermined optical characteristics; forexample, flakes may be optically variable changing color with a changein angle of incident light, or flakes may be diffractive, or may havecovert symbols therein or thereon, or the flakes may simply bereflective or absorptive. In some instances, optical effect flakes havea combination of optical effects, for example, they may be diffractiveand color shifting, or they may be diffractive and reflective, ordiffractive and highly absorptive depending upon the desired effect.Furthermore, flakes having different optical effects may be mixedtogether in desired ratios. Pigments that may be added include thosebased on interference, for example mica based pigments, Fabry Perot typepigments, liquid crystal type pigments, including those that color shiftwith viewing angle, non- shifting pigments like gold and nickel, andother metallic flakes.

In one embodiment of the present invention, the optically variable inkis printed onto a substrate such as a banknote or any other securitydocument.

The substrate supporting the optically variable structure is eitheropaque or light-transmissive in various embodiments of the presentinvention.

FIG. 1 a illustrates a process of manufacturing a first portion of achromagram in accordance with the teachings of this invention. Indiffractive structure 10 a, substrate 12 having region 14 impressed witha hologram, is partially coated with a pattern of highly reflectivealuminum 16 preventing light from passing therethrough. Therefore, whenthe structure is viewed from the top side, a highly reflective surfaceis seen where the Al coating 16 is present. Substrate 12, aresin/hardcoat layer in which the embossing 14 is impressed, may have anoptional protective coating 28 on its surface, whereon one or moreletters, a logo or other indicia 19 is printed. The uncoated portions 17of the hologram are substantially light transmissive.

Generally, in the prior art manufacture of chromagrams, an opticaleffect coating would be applied directly over the Al, as well as overthe uncoated portions of the light transmissive substrate. However, inaccordance with this invention an entirely separate structure 10 b shownin FIG. 1 b is prepared consisting of a substrate and an opticallyvariable coating, such as a color shifting coating.

FIG. 1 b illustrates a process of manufacturing a second portion of achromagram, optically variable structure 10 b, in accordance with theteachings of this invention. A substrate made preferably of PET is showncoated with a reflector layer 22, a dielectric layer 20 and an absorberlayer 18. A hot stamp adhesive layer 62 which may be 3-10 µm thick isthen applied over the optical stack formed by layers 22, 20, and 18 anddried.

A novel and inventive aspect of this invention is the manufacture of awindowed structure, such as diffractive structure 10 a, and a separateoptically variable structure, such as structure 10 b, wherein the twostructures can be married or bonded together forming a chromagram by theapplication of heat and pressure via hot stamping. Each of the first andsecond structures can vary; several non-limiting examples are giventhroughout this application.

In embodiments of the present application the hot stamp adhesive can beapplied and dried upon either a diffractive structure, structure 10 a inthe aforedescribed example, or an optically variable structure, such as10 b, or both structures, prior to bonding the two structures together.The thickness for hot stamp adhesive may be between 3 µm and 10 µm, withpreferable range 3-7 µm.

Further described embodiments of the present invention shown in FIGS. 2a and 2 b have different optically variable coatings on lighttransmissive substrate 64. Substrate 64 can be either opaque or lighttransmissive. Light transmissive substrate 64 provides for viewing thedevice from both sides, which is advantageous if the optically variablestructure is light transmissive, for example made with a lighttransmissive OV ink or an all dielectric Ab/D/Ab optical stack.

In embodiment shown in FIG. 2 a , substrate 64 is coated with reflectivelayer 22, dielectric layer 20 and absorber layer 18 forming opticallyvariable color shifting foil 23. Substrate 12, which can be aresin/hardcoat layer, has grating 14 thereon partially coated with apattern of highly reflective coating 16 in contact with portions of thegrating 14, for preventing light from passing therethrough. Resin layer12 is optionally covered with protective light transmissive layer 28with opaque indicia 19 printed thereon.

FIG. 2 a is the result of adhesively joining structures 10 a and 10 btogether. Preferably, grating 14 is embossed onto substrate 12 andcovered with patterned demetallized aluminum 16, then the demet hologramis hot stamped or hot roll nipped to the optical stack using clear hotstamp adhesive 62. All that is required to form a chromagram once thestructures 10 a and 10 b are brought together is aligning substrates 12and 64 so that they are in registry and then the application of heat andpressure in a hot stamp machine.

Preferably, reflective layer 16 is windowed, so that substrate 12 hasone or more regions 100 thereon embossed and covered with reflectivematerial, said regions separated by regions 17 shown in FIG. 1 a , notcovered with aluminum and can be either embossed or not-embossed. It iseasier to emboss the whole region and then pattern the Al and then putdown the optically matching adhesive. Alternatively, the continuousreflective coating is shifted to one side, the resulting structure hasplanar reflective coating over non-embossed regions providing highlyreflective mirror-like portions of the image as an additional opticaleffect.

The structure shown in FIG. 2 a , when viewed from the top, provides acombined optical effect including a holographic image having windowswherein a color shifting background shows. The combined optical effectis added by printed indicia. When the structure shown in FIG. 2 a isviewed through substrate 64, which should be light transmissive for thispurpose, just a metallic look arising from the opaque reflector isvisible. If the reflector is semi-transmitting, i.e. the thickness ofthe reflector layer is below the opaque point, then one would see acolor shift with a faint reflection hologram showing through at certainlocations where aluminum 16 is present. In between the faint reflectionhologram replicated by aluminum 16 down one would see images fromindicia 19.

Another embodiment of the present invention shown in FIG. 2 b is similarto the embodiment shown in FIG. 2 a in many respects, however has firstsubstrate 64, preferably made of PET, coated with color shifting flakes35 in carrier 34, by way of example an adhesive or acrylic- orurethane-based ink, hot stamped to the same upper structure as in FIG. 2a using a hot stamp adhesive 62. After the ink has dried and cured, thusforming a color shifting coating, a hot stamp adhesive 62 is applied andcured. To form a Chromagram, the coated first substrate having the hotstamp adhesive 62 is bonded with a second substrate covered with thesame layers as in the embodiment shown in FIG. 2 a .

With reference to FIG. 2 e , in another embodiment of the presentinvention, substrate 68 is a banknote or any other type securitydocument. A security structure is formed by printing a color shift inkonto banknote 68 as a background color, and then hot-stamping a demethologram, preferably embossed onto resin/hardcoat layer 12 and supportedby carrier sheet 66, over the ink using transparent hot stamp adhesive62. Optionally, adhesive 62 contains other particles or flakes to modifythe color of the color shift ink or as a covert security feature. By wayof example, adhesive 62 may contain fluorescent materials, covertcharms, such as disclosed in U.S. Pat. Application 20050037192 byArgoitia et al, upshift phosphors, interference pigments like mica-basedinterference flakes, and non-shifting pigments or dyes. The covertflakes are detectable under a microscope, whereas for the fluorescentand phosphor materials, irradiation of the device by UV or IR light isrequired to activate those features. Since resin/hardcoat layer 12 isquite thin, preferably less than 3 microns, the UV or IR light is ableto penetrate to the particles in adhesive 62. In FIGS. 2 e, a releaselayer, resin layer and hard coat are shown as one layer 12 providingfunctionality of each of the three layers. In other embodiments, layer12 is replaced by any combination of separate layers: a resin layer forembossing, a release layer for releasing the demet hologram from carriersheet 66, and a hard coat layer for durability of the transferreddevice. The adhesive layer 62 which couples the optically variable anddiffractive structures is an internal adhesive layer of the Chromagramdevice; an external layer of adhesive may be applied e.g. to thesubstrate 68 (its lower surface with reference to FIG. 2 e ) foradhering the Chromagram device to an object.

In another embodiment of the present invention, similar to thestructures shown in FIGS. 2 a and 2 b , an OV structure used in place ofstructure 10 b is transparent. By way of example, the transparent OVstructure is one having a low density of optically variable flakesincorporating opaque Fabry Perot filters, or one based on all dielectrictransparent optically variable flakes, or like one described in U.S.Pat. No. 5,278,590. When this construction is viewed through the OVfilm, a superposition of the holographic and optically variable effectsis visible. In essence, the rainbow of colors that were in the initialhologram has been modified by the OV structure, such as an opticalstack, whereby some colors are accentuated and some are suppressed.Actually, the hologram can be viewed from both sides; on one side theoriginal hologram can be seen combined with OV background in windows ofthe reflective layer covering the hologram, and on the other side, thesuperposition of the hologram and the optical stack can be seen throughthe OV film.

In FIG. 2 c , covert flakes 45 that cannot be seen with the unaided eyeare mixed into the hot stamp adhesive 40 used to bond the two structurestogether as in the previous embodiments. The examples of covert flakesinclude, but not limited to, charms or taggants as taught in U.S. Pat.Application Publication No. 2006/0035080 incorporated herein byreference, shaped pigments as disclosed in U.S. Pat. Applicationpublication No. 20060035080, magnetic flakes, fluorescent pigments,standard UV activated to form visible light, or specialized anti-Stokesmaterials UV activated to form visible light.

These covert flakes serve as a means of authentication. If the covertflakes provide an optical effect, for example under a microscope orbeing IR activated, additionally to holographic effects exhibited bythis structure, though the windows where the Al coating is missing,covert flakes 45 can be seen on color shifting background.

In another embodiment, optically variable flakes are added to adhesive40 at low concentrations so that the OV foil colors are modified whenviewing from the top.

According to another embodiment of the present invention, FIG. 2 d ,depicts a security article 150 including a light transmissive substrate12 with an optical interference pattern 14 and a color shifting opticalcoating 156 that is laminated to substrate 12 by way of an adhesivelayer 62. The optical coating 156 includes and absorber layer 18,dielectric layer 20, and a reflector layer 22. The optical coating 156is deposited on carrier sheet 64 to form a prelaminate structure priorto being laminated to substrate 12. The prelaminate structure issubjected to a laser imaging process to form both laser ablated image118 as well as laser scribed number 122. As shown in FIG. 2 d , theoptical coating 156 is laminated to substrate 12 so as to be adjacent tooptical interference pattern 14 such as a holographic or diffractivepattern.

The structure shown in FIG. 2 d , when viewed from the top, provides acombination of an opaque image, that may be reflective, formed bypattern 14, a color-shifting background visible in the windows ofpattern 14, and covert flakes which may be added to adhesive 62. Whenthe structure is viewed from the opposite side, laser ablated image 118and laser scribed number 122 are visible on the substrate 64 of thereflective surface of the OV stack if substrate 64 is transparent. Ifhologram 14 is of the transmissive type, for example relief is coatedwith a high index layer of ZnS (not shown), then the laser ablated imageand the number will also be visible from the top.

Conveniently, the aforedescribed manufacturing process allows the firstand second substrates to be manufactured in two different facilities andstored in rolls to be united later.

Conveniently, the second substrate may have any type of optical effectcoating thereon that can be seen through windows in the first substrate.Conveniently any of these first windowed substrates can be married tothese second coated substrates at a later time or immediately, by way ofhot stamping the two together or by hot roll laminating.

In another embodiment of the present invention, alternatively tohot-stamping, a UV activated adhesive is used to bond the two structurestogether. By way of example, an optically variable foil printed with anadhesive is brought together with a laminating sheet containing thedemet hologram; the adhesive is then cured by irradiating the laminatingsheet with UV light, wherein the laminating sheet has a transparent orat least UV light - transmissive substrate. One way to overcome theobstacle to UV light posed by the reflective metal covering thehologram, is to use a patterned or windowed reflective layer whereinareas covered with metal are very narrow, estimated to be less than 2microns, so that UV light can cure the adhesive by coming in at anangle. Another way is to use a semitransparent reflective layer in theOV structure or to use e-beam curing.

In one embodiment of the present invention, shown in FIG. 3 a ,optically variable structure 23 is laminated onto grating 14 usingadhesive 62, wherein grating 14 is supported by, or formed therein,hardcoat/resin layer 70 and covered with layer of high refraction indexmaterial 50. The structure of this embodiment provides a color shiftingholographic image by combining the effects of the optically variable anddiffractive structures. A transparent OV foil can be used in place ofstructure 23.

In another embodiment of the present invention shown in FIG. 3 b ,optically variable foil 23 is laminated using adhesive 62 onto grating14 covered by patterned reflective layer 16, wherein grating 14 issupported by, or formed therein, hardcoat/resin layer 70 and coveredwith layer of high refraction index material 50. By as of example, OVfoil 23 is a transparent all dielectric color shift with angle coatingor one based on a semi-transparent/dielectric/semi-transparent colorshift filter. When viewed from the top, as shown in FIG. 3 b , thisstructure provides a combined optical effect, wherein a specularholographic image formed by light reflected from opaque metallic layer16, is complemented by a lower reflecting holographic image with a colorshifting background from the OV foil 23 formed by light reflecting fromthe regions where reflective layer 16 has windows.

In a structure similar to the structure shown in FIG. 3 b but without ahigh refraction index coating, regions wherein reflective layer 16 haswindows may show very weak holographic effects. This is very muchdependent upon the of index matching between the coating underlying thenon-aluminized portion of the hologram and the adhesive. If there is arefractive index differential of at least 0.2 for the real part of therefractive index, then some holographic effects will be seen. Thegreater the refractive index differential, the more clearly the hologramwill be seen. By way of example, a refractive index differential of 0.8,between a substrate with n=1.5 and high index coating with n=2.3,provides brightness to a transparent hologram. In contrast, if therefractive index of the coating is matched, then no holographic effectswill be seen in the windows.

In reference to FIGS. 3 a and 3 b , high refraction index coating 50 hasan index of refraction no less than 1.65. Suitable examples of such ahigh index transparent layer include TiO₂ or ZnS.

In one embodiment of the present invention, adhesive layer is patternedso that the diffractive structure has regions not bonded to theoptically variable structure.

In another embodiment of the present invention, the adhesive layer ispatterned so that one of the structures, by way of example a OV foil, isbonded to the substrate supporting the second structure, a hologram inour example, forming a frame, or a part of it, around the hologram.

In one embodiment, shown in FIG. 4 , diffractive structure 60 isadjacent to substrate 12, but smaller, so that the top surface ofsubstrate 12 has regions which are not covered with diffractivestructure 60. Instead, at least some of these regions are covered withadhesive material thus forming patterned adhesive layer 63 for bondingoptically variable foil 23 to substrate 12, whereas diffractivestructure 60 is not adhesively bonded to adjacent layers, but is coupledto them by the surrounding adhesive. The pattern of adhesive layer 63can vary, in particular, adhesive 63 can form a frame around diffractivestructure 60 or, in case of elongated hologram 60, adhesive 63 isapplied along two longer sides of hologram 60.

In one embodiment of the present invention, comprising a demetallizedhologram hot stamped onto an optically variable foil, a patterned layerof color shifting ink is deposited underneath the demet hologram. Thisallows the color shift from the foil to show though to the observer. Theflakes of the optically variable ink are generally opaque so that acontinuous coating of ink would block out the underlying foil.Alternatively, the color shifting ink has a low concentration of flakesso that the color shift of the foil could still be seen though theoptically variable ink; the foil colors are modified by the partiallytransparent optically variable ink. Alternatively, a patterned layer ofthe optically variable ink is deposited on the top side of the demethologram, so that both the color shift from the ink and from the OV foilare visible.

Referring now to FIG. 5 a poker chip is shown having covert flakesbearing indicia in the form of a Euro symbol and a $ symbol that is onlyvisible to the human eye with about 100 times magnification. Preferably,these covert flakes are provided within the hot stamp adhesive on one ofthe two optical structures.

What we claim is:
 1. A method of manufacturing a device for providing animage having an optically variable feature, comprising: a) providing adiffractive structure for forming at least a portion of the image; b)providing an optically variable structure distinct from the diffractivestructure, for providing the optically variable feature to the image,wherein the optically variable structure changes color with a change inangle of incident light, and wherein the optically variable structurecomprises a first reflector layer, an absorber layer, and a dielectriclayer between the reflector and absorber layers; c) covering thediffractive structure or the optically variable structure with anadhesive; d) after steps (a)-(c), activating, with energy, the adhesiveand coupling the diffractive structure and the optically variablestructure together in a predetermined mutual arrangement, wherein theenergy activated adhesive forms a layer; wherein the diffractivestructure comprises a relief pattern and a high refraction index layermade of a material having an index of refraction no less than 1.65; andwherein the diffractive structure comprises a patterned opaque coatingso that the diffractive structure has opaque regions and lighttransmissive regions.
 2. The method as defined in claim 1, wherein theopaque regions are configured for preventing light incident on thediffractive structure from propagating through to the optically variablestructure via the layer of the energy activated adhesive, and the lighttransmissive regions are configured for allowing light incident on thediffractive structure to propagate through to the optically variablestructure via the layer of the energy activated adhesive.
 3. The methodas defined in claim 1, wherein in step (a) comprises providing a secondreflector layer to the diffractive structure.
 4. The method as definedin claim 3, wherein the second reflector layer is partiallydemetallized.
 5. The method as defined in claim 4, wherein the secondreflector layer is segmented so that the reflector layer has one or morelight transmissive windows, so that the optically variable structure isvisible through said windows.
 6. The method as defined in claim 3wherein the optically variable structure comprises a coating with aplurality of multilayer optical interference flakes therein or thereon.7. The method as defined in claim 1, wherein step (a) comprisesproviding a substrate having a first side supporting the diffractivestructure, wherein the first side of the substrate has a first regionwherein the diffractive structure is therein or thereon, and the firstside of the substrate has a second region wherein the diffractivestructure is absent, and in step (c) the layer of the energy activatedadhesive is adjoined to the first side of the substrate so that theoptically variable structure is adhesively bound solely to the substrateand coupled to the diffractive structure by the surrounding adhesive. 8.A device manufactured by the method defined in claim
 1. 9. The method asdefined in claim 1, wherein the diffractive structure includes a gratingto form a light transmissive region for allowing light incident on thediffractive structure to propagate through to the optically variablestructure via the layer of the energy activated adhesive.
 10. The methodas defined in claim 1, wherein the diffractive structure includesindicia.
 11. The method as defined in claim 1, wherein the diffractivestructure includes a substrate having the grating impressed on a surfaceof the substrate.
 12. The method as defined in claim 1, wherein thediffractive structure includes a protective coating.
 13. The method asdefined in claim 1, wherein the adhesive includes covert flakes.
 14. Themethod as defined in claim 13, wherein the covert flakes include charms,taggants, shaped pigments, magnetic flakes, or fluorescent pigments. 15.The method as defined in claim 1, wherein in step (c) the adhesivecovers the diffractive structure or the optically variable structure ina pattern.
 16. The method as defined in claim 15, wherein thediffractive structure has regions not bonded to the optically variablestructure based upon the pattern.
 17. The method as defined in claim 15,wherein the pattern of adhesive forms a frame around the diffractivestructure.